HFC components in general have a reinforcing fiber structure which is saturated or impregnated with a resin which is hardened during the process of manufacture of the component. The reinforcing fiber structure is constructed, e.g., from one or more blanks of a two-dimensional, web-like reinforcing fiber material. The blanks are here arranged in one or more layers. The fiber architecture of the reinforcing fiber structure, i.e., in particular a predetermined fiber orientation and/or fiber distribution, as well as a predetermined layer structure of the blanks used and hence of the whole reinforcing fiber structure, is of particular importance for the desired properties of the HFC component, e.g. as low a weight as possible with strength as high as possible.
To obtain a high degree of prefabrication and hence rational production, it is desirable to provide the reinforcing fiber structure as far as possible as a prefabricated subunit in the form of a preform of reinforcing fiber material. For two-dimensional or shell-shaped or cup-shaped open fiber-composite components, this is relatively easy to achieve. The manufacture of HFC components and their preforms of reinforcing fiber material, on the other hand, is comparatively complicated and expensive, sometimes even highly problematic. Particularly in the case of complex HFC components, known technologies are up against their limits; and it is difficult or often impossible to manufacture complex HFC components of this kind with optimized fiber architecture.
It is known that ordinary HFC components can be manufactured by a tube-blowing RTM method. Here, tube-shaped preforms of reinforcing fiber material which are designed as hollow profiles and which can be made by circular knitting, circular weaving or braiding, are used. A molding tube is laid in the hollow preform which has a closed cross-sectional profile, and the preform is laid in an injection mould. Then the molding tube is inflated. Next resin is injected into the injection mould, i.e. between the inner circumferential surface of the mould and the outer circumferential surface of the molding tube, and the resin is hardened. It is obvious that with this technique only HFC components with a single hollow chamber can be made. Furthermore, the fiber architecture obtainable is greatly predetermined or restricted by the above-mentioned manner of manufacturing the preform, and so cannot be further optimized. In particular, reinforcing fiber structures or preforms which are constructed from several single layers of reinforcing fiber material with different or considerably diverging fiber orientation, cannot be made by this method. A prefabricated subunit with a fiber architecture which is optimized or adaptable to the most varied component geometries cannot therefore be achieved.
Tests were performed to produce, by this tube-blowing RTM method, HFC components which have at least two hollow chambers located adjacent to each other, which are separated from each other by an integral, rib-like or web-like partition (hereinafter called a rib for short). However, it turned out that, on account of the fiber architecture described above, which is fixed by manufacture of the tube-like preform, the rib can be only inadequately integrated in the tube-like reinforcing fiber structure or positioned in it. After a molding tube has been arranged in each of the two hollow chambers and inflated inside the injection mould and the resin has been injected, it further turned out that at this stage of the process too the predetermined position and precision of shape of the rib could not be ensured and the preform showed unstable behavior.
The problems described above are in practice avoided by a method which uses at least two adjacent, solid molding cores for fixing the position and shape of a rib/partition in a three-dimensional reinforcing fiber structure which forms a three-dimensional, hollow preform of reinforcing fiber material corresponding to the shape and dimensions of the HFC component to be manufactured. With this method two-dimensional, web-like reinforcing fiber material is cut to size and serves to form at least one planar, single- or multi-layer blank of a reinforcing fiber structure of the preform. The blanks are draped in an injection mould or stitching manufacture means to form the three-dimensional hollow preform of reinforcing fiber material. Within the framework of this process, the rib/partition from a portion of the blank is also draped. The at least two molding cores, the shape and dimensions of which are adapted to the respective hollow chamber of the fiber-composite component, are arranged in such a way that the regions of reinforcing fiber material provided for the rib/partition run exactly between the molding cores. As a result, the position and shape of the rib/partition are fixed in the three-dimensional reinforcing fiber structure and also in the injection mould.
This technique does of course allow the manufacture of complex HFC components with an optimized fiber architecture, but is very elaborate and requires the manufacture and use of molding cores which must later be removed again from the hardened HFC component. Furthermore, it turned out that during resin injection, in spite of the molding cores, there can be unwanted displacement or mutual displacement of the fiber layers of the preform or its reinforcing fiber structure, particularly in the region of the rib/partition. This in turn results in a disadvantageous change in the predetermined fiber architecture.